/*_############################################################################
  _## 
  _##  SNMP4J 2 - CounterSupport.java  
  _## 
  _##  Copyright (C) 2003-2011  Frank Fock and Jochen Katz (SNMP4J.org)
  _##  
  _##  Licensed under the Apache License, Version 2.0 (the "License");
  _##  you may not use this file except in compliance with the License.
  _##  You may obtain a copy of the License at
  _##  
  _##      http://www.apache.org/licenses/LICENSE-2.0
  _##  
  _##  Unless required by applicable law or agreed to in writing, software
  _##  distributed under the License is distributed on an "AS IS" BASIS,
  _##  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  _##  See the License for the specific language governing permissions and
  _##  limitations under the License.
  _##  
  _##########################################################################*/

package org.snmp4j.mp;

import org.snmp4j.event.*;
import java.util.*;

/**
 * The <code>CounterSupport</code> class provides support to fire
 * {@link CounterEvent} to registered listeners.
 * @author Frank Fock
 * @version 1.0
 */
public class CounterSupport {

    protected static CounterSupport instance = null;
    private transient Vector<CounterListener> counterListeners;

    protected CounterSupport() {
    }

    /**
     * Gets the counter support singleton.
     * @return
     *    the <code>CounterSupport</code> instance.
     */
    public static CounterSupport getInstance() {
        if (instance == null) {
            instance = new CounterSupport();
        }
        return instance;
    }

    /**
     * Adds a <code>CounterListener</code>.
     * @param listener
     *    a <code>CounterListener</code> instance that needs to be informed when
     *    a counter needs to be incremented.
     */
    public synchronized void addCounterListener(CounterListener listener) {
        if (counterListeners == null) {
            counterListeners = new Vector<CounterListener>(2);
        }
        if (!counterListeners.contains(listener)) {
            counterListeners.add(listener);
        }
    }

    /**
     * Removes a previously added <code>CounterListener</code>.
     * @param listener
     *    a <code>CounterListener</code> instance.
     */
    public synchronized void removeCounterListener(CounterListener listener) {
        if (counterListeners != null && counterListeners.contains(listener)) {
            counterListeners.removeElement(listener);
        }
    }

    /**
     * Inform all registered listeners that the supplied counter needs to be
     * incremented.
     * @param event
     *    a <code>CounterEvent</code> containing information about the counter to
     *    be incremented.
     */
    public void fireIncrementCounter(CounterEvent event) {
        if (counterListeners != null) {
            for (CounterListener l : counterListeners) {
                l.incrementCounter(event);
            }
        }
    }
}
